The present invention relates to the construction of concrete piling foundations and more particularly to the modular construction of in-place concrete piling foundations having a uniform height above reference terrain level.
Cast reinforced concrete piles are widely used as foundations in the construction of buildings, bridges and other structures. Due to their extremely heavy weight and comparatively low resistance to tensile bending forces, concrete piles are usually pre-formed in short lengths or sections, either with or without pretensioning, at a fabrication yard and, thereafter, the pre-formed sections are transported to the construction site whereat they are disposed vertically and driven to bearing depth in terrain by suitable pile driving equipment. For most construction, it is customary to splice-up the pre-formed sections one to the other in end-to-end relation to form an elongated continuous pile and this may be accomplished either prior to or during the pile driving operation. Known relevant disclosures of pile splicing-up techniques and related procedures include:
Cadwell, U.S. Pat. No. 731,752 PA0 Young, U.S. Pat. No. 3,338,058 PA0 Grazel, U.S. Pat. No. 3,545,214 PA0 Grazel, U.S. Pat. No. 3,593,532 PA0 Shibuya et al., U.S. Pat. No. 3,963,056 PA0 Dougherty, U.S. Pat. No. 3,988,899 p0 Young, U.S. Pat. No. 4,009,550 PA0 Poma, U.S. Pat. No. 4,018,056
Certain problems, however, have remained in the construction and use of concrete pile sections, particularly with respect to the fact that the vertical distance to bearing depth in terrain varies considerably, even within a fairly confined geographical area. Accordingly, the uppermost part of the respective piles must be cut off with jackhammers and the like in order to obtain a finished piling foundation of uniform height above reference terrain level. Given the high acquisition and disposal costs associated with these cut off parts, which cannot be economically re-used, this present technique inherently requires considerable waste. The problem is very much aggravated by the fact that construction efficiency requires section lengths generally in the range of 10-30 feet, of which, in some cases only a few inches of the uppermost section are required to drive the pile to bearing depth in terrain.
Substantially hollow, preformed piling sections have also been presented which are spliced-up and driven to bearing and, thereafter, filled with a hardenable plastic material such as concrete to form a finished piling. Notable examples of the hollow piling technique include Kohn U.S. Pat. No. 2,430,879, Kelly et al. U.S. Pat. No. 3,899,891, and Le Clercq U.S. Pat. No. 4,018,055. This approach also involves cutting off the uppermost part of the uppermost section, and hence economical waste. Further, any reduction in economic waste, because of the substantially hollow construction employed, is severely limited by the relatively thick wall construction required to withstand the impacting forces applied to the sections as they are driven to bearing depth.
It has also been suggested (Kahn, previously cited) to fasten a threaded device to the uppermost pile portion and, thereafter, thread a shell enclosure atop the pre-formed pile portion. This shell enclosure can be cut off and filled with a hardenable plastic material to buildup a finished piling foundation of uniform height above reference terrain level. This approach, however, inherently requires that the cast-in-place portion be circular in cross section and that considerable care be taken to avoid damage to the threads of the fastening apparatus. More importantly, the installation of the threaded base portion atop the pre-formed pile portion and the subsequent operations required to thread the shell enclosure in the threaded base portion requires considerable effort and time. Obviously, at the pile drive site, in outdoor conditions, it is essential for cost savings that the splicing-up and building-up be as speedy as possible.
It is also important to consider that the widespread use of concrete piles as foundation structures has resulted largely from the high load bearing capability of concrete in compression. A concrete structure, however, particularly an elongated piles, has comparatively low load bearing capability other than in axial compression. Accordingly, when lateral loading forces are applied to the concrete piles, such as during the threading operation presented by Kohn, or the application of non-axial driving forces, it tends to produce spalling of the outer surface of the piling thereby creating the risk that interconnecting reinforcing bars will be subjected to corrosive elements. This problem is especially aggravated by the fact that the spalling often does not complete until after the interconnecting joint has been driven into the terrain thereby precluding effective inspection and repair. It will be seen that such subterranean defects will unduly shorten the load-bearing life of the resultant piling foundation and necessitate complex and costly repair operations.